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New Study Refines View of Sarin Attack in Syria

A new analysis of rockets linked to the nerve-agent attack on Damascus, Syria, in August has concluded that the rockets were most likely fired by multiple launchers and had a range of about three kilometers, according to the two authors of the analysis.

The authors said that their findings could help pinpoint accountability for the most lethal chemical warfare attack in decades, but that they also raised questions about the American government’s claims about the locations of launching points, and the technical intelligence behind them.

The new analysis could point to particular Syrian military units involved, or be used by defenders of the Syrian government and those suspicious of the United States’ claims to try to shift blame toward rebels.

The rockets in question were not seen before the Syrian civil war. There is little publicly available information about their internal construction, their manufacturing provenance or their flight characteristics.

That attack is broadly believed to have caused at least hundreds of civilian deaths. It led the Obama administration, which blamed the government of President Bashar al-Assad, to threaten military action. That threat was deferred in mid-September after Russia and the United States reached an agreement to dismantle the Syrian government’s chemical weapons program.

The authors of the new analysis —Theodore A. Postol, a professor of science, technology and national security policy at the Massachusetts Institute of Technology, and Richard M. Lloyd, an analyst at the military contractor Tesla Laboratories — evaluated the exteriors of the implicated rockets, visible in videos and photographs. The analysis suggested that they were propelled by motors taken from a common family of 122-millimeter conventional artillery rockets known as the BM-21, the authors said.

The BM-21 line is a globally abundant system of ground-to-ground rockets, colloquially called Grads, that originated in the Soviet Union but have been reproduced and updated by many countries, including post-Soviet Russia, China, Egypt and Iran. Both the Syrian army and the rebels possess them.

An examination of the territory to the northwest of the cluster of reported impact strikes shows many positions that have been firmly under military control throughout 2013, including factories and a bus station complex that are part of Mr. Assad’s defense around his seat of government.

Eliot Higgins, a blogger who has collected and analyzed many online videos related to the attack, the munitions and the Syrian government’s military positions in Damascus, said the new analysis of the rockets’ range aligned with assertions that the government was culpable.

“A range of beyond 2.5 kilometers would put potential launch sites in an area between Jobar and Qaboun, to the north and northwest of the impact locations, that has been a hive of government activity for months,” Mr. Higgins wrote in an email on Friday.

But the analysis could also lead to calls for more transparency from the White House, as Dr. Postol said it undermined the Obama administration’s assertions about the rockets’ launch points.

On Aug. 30, the White House released its assessment of the attack, saying that, among other forms of intelligence, “satellite detections corroborate that attacks from a regime-controlled area struck neighborhoods where the chemical attacks reportedly occurred.”

Photo

An image taken by local activists in Damascus shows the remains of a rocket implicated in a chemical attack in August.

Dr. Postol said those statements created a public impression that the rockets had been launched from areas at the center of government control.

“It is clear that if the U.S. government’s claims that the allegedly observed launches came from ‘the heart’ of Syrian government controlled areas, there is a serious discrepancy between the meaning of this claim, the technical intelligence it relies on, and the technical properties of this munition,” he wrote.

Using published data about characteristics of motors in various Grad rockets and derivatives, Dr. Postol and Mr. Lloyd calculated potential maximum ranges for the sarin-filled rockets, with an emphasis on a common Grad variant’s motor.

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“The dimensions of the inserted rocket motor very closely match the dimensions in the 9M22-U artillery rocket,” Dr. Postol wrote in an email on Thursday. “If the inserted motor is the same as the standard 9M22-U motor, then the maximum range of the munition would be no more than three kilometers, and likely less.”

That would be less than the ranges of more than nine kilometers calculated separately by The New York Times and Human Rights Watch in mid-September, after the United States had dropped its push for a military strike. Those estimates had been based in part on connecting reported compass headings for two rockets cited in the United Nations’ initial report on the attacks.

The published range for a 9M22-U rocket is about 20 kilometers, or 12.4 miles. But the Syrian rockets carried a bulky and apparently flat-nosed warhead — Dr. Postol called it “a soup can” — whose range would have been undermined by its large mass and by drag, the authors said.

Depending on the motors propelling different Grad models, the projected maximum ranges can vary from 2.5 to 3.5 kilometers, or 1.5 to 2.2 miles, Dr. Postol and Mr. Lloyd said.

The longer estimates seem unlikely, Dr. Postol said, because as a sarin-filled rocket was pushed to greater air speeds by a more powerful motor, the stresses created by its non-aerodynamic shape could cause it to tumble or break apart.

“The line of impacts suggests a launcher that changed loft angle,” Dr. Postol wrote. “This is consistent with a strategy aimed at spreading the nerve agent over a wide area.”

The new analysis has limits. It relies on secondhand measurements of and assumptions about the rockets’ components and construction, but no handling, X-rays or other examination of the real items. The central claim, about a particular rocket-motor insert, regards an item that has not yet been seen in any publicly available images.

Nonetheless, a core assertion in the two authors’ previous analysis of the sarin-filled rockets, also based on dimensions, has stood for months.

That study proposed that the warheads contained a large volume, about 13.2 gallons, of sarin. The United Nations implicitly seconded that suggestion when it included a similar estimate in its own report in September.

The assumption that the warheads contained a large volume of nerve agent also helped shape another prominent analyst’s assertion that the details of the Aug. 21 attack implicated the Syrian government.

A version of this article appears in print on December 29, 2013, on Page A10 of the New York edition with the headline: New Study Refines View Of Sarin Attack in Syria. Order Reprints|Today's Paper|Subscribe